FIGURE 2.

Concentration-dependent effect of histamine on Ca²⁺ signalling in WI-38 human lung fibroblasts. (A) Typical intracellular Ca²⁺ recordings in WI-38 cells loaded with FURA-2/AM exposed to different histamine concentrations ranging from 100 nM to 1 mM. The baseline of Ca²⁺ tracings has been shifted to avoid their overlapping for representation proposes. (B) Non-cumulative concentration-response relationship. Data points are the mean ± SE of the initial Ca²⁺ peak amplitude (black circles) or plateau amplitude (blue circles) plotted against the logarithm of histamine concentration. The continuous curves were obtained by fitting the data to Eq. 1, as shown in Materials and methods, which yielded EC₅₀ values of 4.96 and 5.25 µM for peak amplitude (black line) and plateau amplitude (blue line), respectively. Data points were obtained of at least 19 cells. (C) Percentage of cells that presented each of the Ca²⁺ response patterns indicated in function of histamine concentrations applicated to WI-38 fibroblasts. (D) Data points are the mean ± SE of the number of oscillations measured over the first 400 s after histamine application, plotted against the logarithm of histamine concentration. The continuous curve was obtained by fitting the data to Eq. 1, as shown in Materials and methods, which yielded EC₅₀ values of 2.38 µM.